This research is concerned with the following topics as applied to electrocardiography. 1. The effect of inhomogeneities on the electrocardiogram. This is studied by means of an eccentric spherical heart in a spherical torso which appears both simple yet capable of accounting for the major effects both of structure (geometry) and electrical conductivity of torso inhomogeneities. A spherical harmonic expression has been successfully applied to a two-spheres model which correctly treats the effects of eccentricity of the heart sphere. This is being extended to the five-spheres case which will be utilized to investigate both conductivity and geometry factors. 2. Cardiac activation models are being formulated and examined which correlate cellular and tissue parameters and which include both the electrophysiology and histology as currently understood. These models relate to the anisotropy in conduction velocity as well as the anisotropy in subthreshold space constants and d.c. impedance. In addition to these model studies, suitable electronics for simultaneous recording from 90 sites is complete and will be utilized to investigate the actual spatial potential fields of a dog heart in order to determine the volume distribution of sources throughout the cardiac cycle. BIBLIOGRAPHIC REFERENCES: Plonsey, R., "Physical Principles of Electric Fields." In: Handbook for Engineering in Medicine and Biology (Feinbery and Fleming, eds.), CRC Press, Cleveland, pp. 191-224 (1976). Klee, M. and R. Plonsey, "Stimulation of Spheroidal Cells -- The Role of Cell Shape." IEEE Trans. Biomedical Engr., BME-23:347-354 (1976).